Receiver architecture for the receiving of angle-modulated/angle-keyed carrier signals

ABSTRACT

Carrier signals received by a receiver architecture for an amplitude spectrum of the carrier signal prescribed by the employment of the receiver architecture even given small modulation indices, a low-noise amplifier (VS) preceding a synthesizer (SYN) of the receiver is either turned off dependent on the field strength received with the carrier signal or is fashioned such that the maximum output power of the amplifier (VS) at the possible amplitude spectrum of the carrier signal never lies above the compression point of the mixer/mixers in the synthesizer (SYN).

BACKGROUND OF THE INVENTION

The invention is directed to a receiver for the reception ofangle-modulated/angle-keyed carrier signals.

Receivers of the type referred to above are utilized everywhere incommunications technology where an HF signal serving as carrier andconnected by modulation with an analog or digital LF signal containingthe information to be transmitted is in turn to be edited. A distinctionis made between an analog or digital modulation or, respectively,demodulation type dependent on the employment of an analog or of adigital LF signal. The term “keying” is employed for the digitalmodulation or, respectively, demodulation for distinguishing between thetwo types.

There are respectively different modulation or, respectively,demodulation forms for each modulation or, respectively, demodulationtype (analog or digital). A distinction is thereby made between anamplitude, frequency and phase modulation or, respectively, amplitude,frequency and phase demodulation. Over and above this, thereby arenumerous derivatives of the aforementioned modulation or, respectively,demodulation forms (for example, GFSK, GMSK, etc.), particularly giventhe digital modulation or, respectively, demodulation type. Frequencyand phase modulation or, respectively, frequency and phase demodulationis also referred to as angle modulation or, respectively, demodulation.

The above comments refer to a single HF signal to be modulated or,respectively, demodulated that is available to a limited subscribercircle for the message transmission in a message system, for example ina mobile radiotelephone system or cordless telecommunication system.

In order to augment the subscriber circle, the plurality of dimensionsfor the analog or digital modulation or, respectively, demodulation isincreased. The time and/or frequency domain are preferably utilizedtherefor. Alternatively thereto, it is also possible to additionallyutilize the transmission channel defined by the time and frequencydomain with different codings. In the utilization of the time and/orfrequency domain, one speaks of a TDMA and/or FDMA method (Time DivisionMultiple Access; Frequency Division Multiple Access). In the utilizationof the time and frequency domain in conjunction with the employment ofdifferent codings, one speaks of a CDMA method (Code Division MultipleAccess).

Receiver architectures for receiving angle-keyed carrier signals whosefrequencies lie in a frequency band between 890 MHz and 960 MHz given aGSM system and in a frequency band between 1880 MHz and 1900 MHz in aDECT system are therefore utilized in mobile radiotelephone technologyaccording to the GSM standard (Groupe Speciale Mobile or Global Systemfor Mobile Communication; see Informatik Spektrum 14 (June 1999) No.3,Berlin, A. Mann, “Der GSM-Standard—Grundlage f{umlaut over (u)}rdigitale europ{umlaut over (a)}ische Mobilfunknetze”, pages 137 through152), including the derivative DCS1800 and the American version ADC andJapanese version JDC, as well as in the cordless telecommunicationstechnology according to the DECT standard (Digital European CordlessTelecommunication, see Nachrichtentechnik Elektronik 42 (Jan/Feb 1992),No.1, Berlin, U. Pilger, “Struktur des DECT-Standards”, pages 23 through29), including the American version WCPS, the CT2 and CT3 standard(Cordless Telecommunication).

When building a receiver—for example, for the aforementioned systems—onegenerally distinguishes between a homodyne receiver (direct receiver) orheterodyne receivers (double detection receivers) with single or doublefrequency conversion. Compared to heterodyne receivers, the homodynereceiver has the advantage that the homodyne receiver can be more highlyintegrated. Compared to the homodyne receivers, the heterodyne receiverhas the advantages that the selectivity can be easily defined by aband-pass filter at the intermediate frequency and the frequency of thevariable oscillator, and that the demodulation occurs at a relativelylow frequency. The homodyne receiver, moreover, is not especiallywell-suited for TDMA systems because the majority of the systemamplification is undertaken in the baseband amplifier. These amplifiers,however, react to very low frequency signals and are therefore verysensitive to transient responses that arise due to switching between atransmission mode and a reception mode in the TDMA systems (see ntz,Vol. 46 (1993) No. 10, pages 754 through 757).

FIG. 1 shows a homodyne receiver (direct conversion receiver) disclosedby Great Britain Reference GB-2,286,950 A1 that contains a one-stagesynthesizer SYN typical for homodyne receivers with a preceding,low-noise amplifier VS and band-pass filter BPF and with a followinglimiting means LE and decoder means DE. Two further components (forexample, an A-component and a B-component) can be generated with thelimiting means LE for an “In Phase” component (I-component) and aquadrature component (Q-component) of the signal to be demodulated,being formed by addition or, respectively, subtraction of theI-component and Q-component. As a result thereof, the angle resolutionis enhanced in the complex I/Q level. For the demodulation in thedecoder means, further, the components (signals) are limited hard(limited), as a result whereof the statusses “1” or “−1” arise for theI, Q, A and B components.

An angle-keyed signal (for example, the GFSK signal) can have anarbitrary angle in the complex level. The current frequency of thecarrier is modified by +Δf or, respectively, by −Δf in GFSK modulationfor the transmission of digital information. The modification by +Δfthereby corresponds, for example, to a logical “1”, whereas themodification by −Δf, logically, corresponds to a logical “0”. In thecomplex level, the frequency shift/modification ±Δf corresponds to arotation of the pointer by Δφ in clockwise direction (for example, givena logical “1”) or, respectively, in counter clockwise direction (forexample, given a logical “0”). The amount of the angle change (frequencychange) is thereby dependent on the modulation index employed. At leastone further coordinate system is generated in order to also be able toidentify slight angle changes of the pointer in the I/Q level. Forexample, this additional coordinate system is formed by the A-componentand B-component.

FIG. 2 shows the complex level with the unit circle and two coordinatesystems, the I/Q coordinate system and the A/B coordinate system, thatare shifted by 45° relative to one another. As a result thereof, theunit circle is divided into eight sectors of equal size. Four quadrantsI, II, III, IV in which the pointer can be located can be recognizedwith each of the two coordinate systems. Two sectors for the possibleposition of the pointer thus derive in each coordinate system. Theactual position of the pointer derives from the meet of two sectors.This is demonstrated with reference to the following example:

A signal to be demodulated or, respectively, decoded exhibits thefollowing status values for the I, Q, A and B components: I=1; Q=1; A=1;B=−1.

According to FIG. 1, the sectors 1 and 2 are possible in this case forthe I/Q coordinate system.

According to FIG. 1, the sectors 1 and 8 are possible in this case forthe A/B coordinate system. The common meet is the sector 1.

Analogous thereto, the allocations “sector—I,Q,A,B status values” can beidentified for the other sectors, these being shown in the followingtable.

I Q A B Sector No. 1 1 1 −1 1 1 1 1 1 2 1 −1 1 1 3 1 −1 −1 1 4 −1 −1 −11 5 −1 −1 −1 −1 6 −1 1 −1 −1 7 −1 1 1 −1 8

All other value combinations are inadmissible.

As already mentioned, the information to be decoded (useful information)is contained in the rotational sense of the pointer. This rotationalsense derives from the current position (current sector) and theprevious position (previous sector). The current sector must thereforebe compared to the previous sector for the demodulation. The rotationalsense derives therefrom, as, thus, does the decision as to whether alogical “0” or a logical “1” was sent. The demodulation is thus reducedto the comparison to a table for determining the current sector and acomparison of this sector to the preceding sector.

The reconstruction of the data is possible when the modulation index isbig enough in order to see to it that a sector is always transgressedor, stated differently, the plurality of sectors (and, thus, the angleresolution) is to be selected such that the minimum angle change(dependent on the modulation index) always produces a change in sector.

The demodulation of an angle modulated/keyed carrier signal with thereceiver disclosed by Great Britain Reference GB-2,286,950 A1 and theabove-described demodulation principle, which can likewise be derivedfrom this publication, is only possible for a limited amplitude spectrumof the carrier signal. The reason for this is that the mixers 28, 30 inFIG. 3 of Great Britain GB-2,286,950 A1 limit the signal given certainsignal amplitudes, and an evaluation of the amplitude informationcontained in the I-component and Q-component is therefore no longerpossible for generating the A-component and B-component.

European Reference EP-0 637 130 A2 discloses a receiver wherein, due toan automatic gain control (AGC), the carrier signals arriving at a mixerstage are controlled such with respect to their amplitude that alimiting effect does not occur in the mixer stage.

Quasi-homodyne receivers that respectively comprise a two-stagesynthesizer have been presented at the ILP Conference, Mar. 9, 1995,University of California, Berkeley, T. Weigandt, S. Mehta, P. R. Gray,“integrated VCO/Synthesizer for DECT/Multi-Standard RF Modems”, and atthe InfoPad Retreat Conference, Jan. 9-1995, University of California,Berkeley, T. Weigandt, S. Mehta, P. R. Gray, “Frequency Synthesis for aMonolithic CMOS RF Transceiver”, whereby a first synthesizer stage isoperated with a constant frequency and a second synthesizer stagefollowing the first synthesizer stage is operated with a variablefrequency.

SUMMARY OF THE INVENTORY

The object underlying the invention is comprised in specifying areceiver for the reception of angle-modulated/keyed carrier signals thatunites the advantage of the high degree of integration in a homodynereceiver with the advantages of a heterodyne receiver and whereby, evengiven small modulation indices, the carrier signals can bedemodulated/decoded for an amplitude spectrum possible due to theemployment of receiver.

In general terms the present invention is a receiver for the receptionof angle modulated/keyed carrier signals. A synthesizer for thesynthetic generation of a base signal to be demodulated/decoded andhaving an I-component and a Q-component from the carrier signal. Alow-noise amplifier precedes the synthesizer. Means for generatingadditional components of the base signal are fashioned such that, basedon the evaluation of an amplitude information contained in theI-component and Q-component, at least one A-component phase-shiftedrelative to the I-component of the base signal and one B-componentphase-shifted relative to the Q-component of the base signal aregenerated. The synthesizer is fashioned two-stage, whereby control meansare allocated to the amplifier with which all carrier signals containedwithin a possible amplitude spectrum and pending at the input side ofthe amplifier are amplified to an amplitude of a signal output at theoutput side of the amplifier to the synthesizer. The amplitude isadequate for the generation of the A-component and of the B-component.The control means are fashioned as a microprocessor allocated to theamplifier that turns the amplifier on or, respectively, off dependent onthe amplitude of the carrier signal adjacent at the input side of theamplifier such that the predetermined amplitude is not exceeded.

Advantageous developments of the present invention are as follows.

The control means are fashioned as a limiting circuit arranged in theamplifier that limits the gain of the amplifier to the amplitudeadequate for the generation of the A-component and the B-component.

The control means are fashioned as a microprocessor allocated to theamplifier that turns the amplifier on or, respectively, off dependent onthe amplitude of the carrier signal adjacent at the input side of theamplifier such that the amplitude adequate for the generation of theA-component and B-component is not exceeded.

The receiver can be used in a DECT-specific cordless telecommunicationsystem, as well as, in a GSM-specific mobile radiotelephonetelecommunication system.

The idea underlying the invention is that either the low-noise amplifierpreceding the two-stage synthesizer of the receiver is turned on and offdependent on the amplitude of the received carrier signal that isadjacent at the input side of the amplifier (for example, by amicroprocessor that, for example, evaluates the field strength of thecarrier signal) and, as a result thereof, the mixer/mixers in thesynthesizer is/are no longer driven into limitation or the amplifier isfashioned such (for example, with an internal limiting circuit) that themaximum output power of the amplifier at the possible amplitude spectrumof the carrier signal never lies above the compression point of themixer/mixers in the synthesizer. The fact that the amplifier limits inthis case is unproblematical because the carrier signal has a constantenvelope at this point in time.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The invention,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures of which like referencenumerals identify like elements, and in which:

FIG. 1 is a block diagram of a prior art homodyne receiver;

FIG. 2 depicts the I/Q coordinate system and the A/B coordinate system;and

FIG. 3 is a block diagram of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Proceeding from the known homodyne receiver according to FIG. 1, FIG. 3shows a receiver modified with respect to the synthesizer SYN thatunites the advantages of a homodyne receiver with those of a heterodynereceiver. The receiver shown in FIG. 3 is therefore also referred to asquasi-homodyne receiver. In order to achieve the high degree ofintegration characteristic of homodyne receivers with the receiver shownin FIG. 3, the local oscillators for the frequency conversion, which aretypical for a homodyne and heterodyne receiver, must be integrated(complete integration).

The problem thereby arises that the realization of the required phasenoise of the oscillator is inadequate. In order to avoid this problem, afirst local oscillator LO1 of a first synthesizer stage SYNS1 in thesynthesizer SYN is operated at a fixed frequency. As a result thereof,the bandwidth of the synthesizer SYN can be selected very big, so thatthe phase noise in the range of interest is essentially determined bythe stability of a reference oscillator (not shown in FIG. 3) that isemployed.

Since the first local oscillator LO1 is not variable in frequency, thedirect conversion architecture typical of the homodyne receiver is notpossible due to the lacking channel selection. The signal received viathe antenna, filtered in the band-pass filter BPF and amplified in thelow-noise amplifier VS (Low Noise Amplifier), for example the DECTsignal given a DECT receiver, is therefore converted onto anintermediate frequency in the first synthesizer stage SYNS1. By contrastto known heterodyne receivers, however, a channel selection is therebynot implemented. In order to suppress the mirror frequencies arising inthe conversion of the reception signal onto the intermediate frequency,a mixer arrangement MA (configuration) with respect to the mixersemployed in this stage is employed in a second synthesizer stage SYNS2following the first synthesizer stage SYNS1, this mixer arrangement MAconverting the reception signal converted onto the intermediatefrequency into the baseband and thereby simultaneously suppressing themirror frequencies that arose in the first synthesizer stage SYNS1. Theconfiguration for the mirror frequency suppression is also referred toas “Image Rejection Mixer” configuration. For the suppression of themirror frequencies, the mixer arrangement MA in the second synthesizerstage SYNS2 is thereby operated by a second local oscillator LO2 that,differing from the first local oscillator LO1, is variable in frequency.As a result thereof, the channel selection or, respectively, channelselecting already addressed above is realized.

The components formed by the mixer arrangement for the mirror frequencysuppression are combined at the output of the second synthesizer stageSYNS2 to form an I-component and a Q-component, analogous to theconditions given homodyne receivers. The channel selection in thebaseband is subsequently realized by low-pass filters in the I-branchand Q-branch, as in the known homodyne receiver of FIG. 1.

Additional components, an A-component and a B-component, can begenerated—in conformity with Great Britain reference GB-2,286,950 A1—byweighted addition or, respectively, subtraction of the I-component andQ-component with the limiting means LE following thereupon. The angleresolution in the complex level can be enhanced by a coordinate systemadditionally obtained in the complex level in this way. Receptionsignals with a small modulation index can thus also be decoded in thedecoder means DE with this improved angle resolution.

So that the filtered reception signal—for example, the DECT signal—amplified by the amplifier VS is not limited by the following mixers ofthe first synthesizer stage SYNS1 given high signal amplitudes of thereception signal and the amplitude information for the initiallydescribed formation of the A-component and B-component is not lost as aresult thereof, the amplifier VS comprises

a) a limiting circuit BS that is fashioned such that the maximum outputpower of the amplifier VS at the possible amplitude spectrum of thereception signal never lies above the compression point of the followingmixers, or

b) a connection to a microprocessor MP that shuts off the amplifier VSgiven high signal amplitudes of the reception signal, for example on thebasis of the evaluation of measured field strengths of the receptionsignal.

When the receiver shown in FIG. 3 is utilized, for example according toInternational reference WO 94/10764 or International reference WO94/10812, in the radio part of a DECT base station of a DECTtelecommunication system, the microprocessor MP can, for example, thenbe the DECT controller DECT-C shown in FIG. 1 of WO 94/10764 or the DECTcontroller or, respectively, main controller M-CT shown in FIG. 1 ofInternational reference WO 94/10812.

The invention is not limited to the particular details of the apparatusdepicted and other modifications and applications are contemplated.Certain other changes may be made in the above described apparatuswithout departing from the true spirit and scope of the invention hereininvolved. It is intended, therefore, that the subject matter in theabove depiction shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A receiver for reception of angle modulated/keyedcarrier signals, comprising: a synthesizer for synthetic generation of abase signal to be demodulated/decoded and having an I-component and aQ-component from a carrier signal: a low-noise amplifier that precedesthe synthesizer; generator for generating additional components of thebase signal, the generator being structured such that, based on anevaluation of amplitude information contained in the I-component andQ-component, at least one A-component, phase-shifted relative to theI-component of the base signal, and one B-component, phase-shiftedrelative to the Q-component of the base signal, are generated; thesynthesizer being a two-stage synthesizer; a first synthesizer stage forsynthetic generation of the I-component and of the Q-component from thecarrier signal, said first synthesizer stage having a first localoscillator operated with a constant frequency; a second synthesizerstage following the first synthesizer stage, said second synthesizerstage having a second local oscillator adjustable with a variablefrequency and a mixer arrangement for suppression of mirror frequenciesin a synthetic generation of a base signal to be demodulated/decoded;the amplifier having a controller with which all carrier signalscontained within an amplitude spectrum and pending at an input side ofthe amplifier are amplified to an amplitude of a signal output at anoutput side of the amplifier to the synthesizer, said amplitude allowinggeneration of the A-component and of the B-component.
 2. The receiveraccording to claim 1, wherein the controller is a limiting circuitarranged in the amplifier that limits gain of the amplifier to theamplitude for the generation of the A-component and the B-component. 3.The receiver according to claim 1, wherein the controller is amicroprocessor allocated to the amplifier that turns the amplifier onor, respectively, off dependent on the amplitude of the carrier signalat the input side of the amplifier such that a minimum amplitude for thegeneration of the A-component and B-component is not exceeded.
 4. Thereceiver according to claim 1 wherein the receiver is utilized in aDECT-specific cordless telecommunication system.
 5. The receiveraccording to claim 1, wherein the receiver is utilized in a GSM-specificmobile radiotelephone telecommunication system.